A little notebook I carry around with me

I work in RF and have to mess around with SMA cables all the time. As a result I carry a 5/16 wrench on my lanyard.

Some antennas have active components (not just preamps) that require some kind of DC voltage to work properly. Pretty common in dedicated GPS antennas. They also have bias ts covering pretty much any band you can think of. Well into the GHz range.